1. Field of the Invention
The present invention relates to brushless motor driving systems and more particularly to a brushless motor driving system which will detect positions of a rotor composed of a permanent magnet by way of magnetic flux sensing elements such as Hall generators to suitably distribute the driving exciting current flown into field coils thereby imparting a rotative force to the motor, wherein alternating signals of low frequencies are applied as a power source, the direction of power supply to the motor being inverted by said alternation to reversely rotate the motor.
2. Description of the Prior Art
In brushless motors of the type which produce rotative torque in a predetermined direction by using field detecting generators such as Hall generators to vary distribution of current flown into driving coils by signals from said Hall generators, the reversible rotation of the motor may not be accomplished by merely inversely switching polarities of the power source as is effected by conventional D.C. commutator motors. This is due to the fact that the rotational direction of a rotor cannot be inverted by mere simple inversion of polarities of the power source because of polarities, etc. of semiconductor elements, which are incorporated in a driving circuit for controlling current flown into the coils. For this reason, in prior art reversibly rotative brushless motors, it is necessary to provide a special inverting circuit in consideration of polarities of D.C. input into Hall generators and operative direction of transistors in the driving circuit, and the inversion and switching mechanism therefor disadvantageously becomes complicated. For instance, the reversible D.C. motor is often used as a servo-motor or as a reference motor for measuring rotative torque of a motor and the like. However, such a prior art D.C. motor requires at least four lead wires in addition to a power supply lead wire in order to reverse the motor and performs its commutating function through non-contact so that, when Hall generators or the like are used, power supply terminals to said Hall generators and output terminals naturally increase. As a result, in the prior art D.C. motors, the number of lead wires connected with a single reversible motor is increasingly required; the working condition at the time of assembly takes a turn for the worse; and it becomes costly. Particularly, in use of the above-described reversible motor as a reference motor for measuring torque, the increase in number of lead wires more than two power supply lead wires hereinbefore described accordingly requires to increase the strength of bundling said lead wires, thus lacking in softness. This has been a fatal drawback causing an error in the measure of torque.